The invention relates to a method for automatic changeover of the workholding device in hobbing machines, and to means for the implementation of such a method.
A significant problem encountered in hobbing machines is that of obtaining an automatic setup for work requiring workholding and location equipment other than that currently fitted; automation of setup is sought to the end of enabling long-term unassisted operation of the machine.
The workholding equipment in modern hobbing machines consists of a rest, associated permanently with the machine and invested with such movement as must be imparted to a workpiece during hobbing, and a device, to which the work is clamped, that can be made fast to and separated from the rest at will.
In machines as currently embodied, the rest and the various devices are provided with tapers, a bore for the rest and a shank for the device, which serve for fitment and location purposes and are intended to permit swift changeover of the device.
For unmanned changeover of the device, use is made of apparatus comprising a mechanical arm which removes the device currently occupying the rest and positions whichever other device may be required for the following hobbing operation. The changeover implemented with such a method is neither simple nor swift however, inasmuch as to accomplish each transfer of a single device, the arm has to move first through a vertical, then through a horizontal direction, and then again through a vertical direction opposed to the first. Even when the arm has finally completed this complicated set of movements, faultless positioning can be hindered by swarf that may have found its way into the tapered bore of the rest during the course of the previous hobbing operation.
In order that such swarf can be removed from the tapered bore of the rest, the machine incorporates a cleaning system whereby oil is caused to circulate, flooding the bore by filling from the bottom upward and ultimately overflowing. This is a system that has proved unsatisfactory for a number of reasons, amongst which, for example, the considerable quantity of oil required, and the fact that such oil contributes to a dirty state of the machine.
A further, and more serious drawback of the cleaning system in question is the fact that swarf often will not be cleared away with the flow of oil, but cling to the locating surfaces of the bore; the presence of such foreign matter constitutes a considerable damage hazard, inasmuch as the replacement workholding device must be removed immediately, and a fresh charge of cleaning fluid sent into the bore. Repeated flooding still does not provide sufficient remedy for the removal of swarf preventing faultless location of the workholding device, however, and the attention of the operator will often be required; this results in drastic loss of a machine's facility for unmanned operation, despite the incorporation of a costly cleaning system.
The object of the invention described herein is that of overcoming the drawbacks described above.